In this study, plant species diversity in Black pine, Red pine, Crimean juniper and oak forests in Dursunbey (Balıkesir) district was associated with some environmental variables and stand characteristics. Diversity calculations were performed at alpha, beta and gamma levels by using alternative indices (Shannon-Wiener, Simpson, Whittaker) and numerical transformations. According to the results of linear correlations and modeling analysis, alpha plant diversity was found to be higher in the forests where black pine (Pinus nigra), red pine (Pinus brutia), and juniper (Juniperus excelsa) species are dominant compared to oaks. In addition, the valley or canyon landforms contributed significantly to the alpha species diversity in these forests. Alternative scales used in the study caused significant differences in beta diversity. In the calculations made according to the data of 4 sub-samples of 20x20m, beta diversity was found to be the highest in oak forests, whereas in the data obtained from the main sample areas of 100x100m, on the contrary, the lowest beta diversity was calculated in oak forests and the highest in black pine forests. The degree of the canopy of the stands made a significant difference in beta diversity. Beta diversity is highest in discontinuous stands (1-10%), and the lowest in full canopy stands (71-100%). The most significant environmental variable for beta diversity was elevation. Changing climatic conditions and geomorphological heterogeneity due to the increase in elevation in the forests of the district have led to an increase in beta diversity. No statistically significant relationship was found between environmental variables and gamma diversity.